There is a known polarizer, obtained on the basis of liquid-crystal solutions of organic dyes as described in WO 94/28073. Polarizer, according to the herein technology, is obtained by application of thin film of liquid crystalline dye solution onto a glass or polymer substrate via one of the known methods. The distinction of this technology lies in that the orientation of the dye molecules occurs in the process of application of the film, so that a thin heat-resistant polarizing coating forms on the substrate immediately after drying. Such films could be used as polarizers in various optical devices. Their application allows creation of new designs of liquid-crystal displays, in which polarizers could form directly on the surface of liquid crystal cell, on the outside as well as on the inside.
In order to increase the mechanical strength of polarizers, render the material water-insoluble and stable with respect to other solvents, and improve thermal stability, the polarizers can be treated with a special solution containing divalent or trivalent metal ions (WO 00/25155). Such a treatment can be effected by immersing of the whole substrate plate with an applied polarizer into an appropriate solution, followed by rinsing in distilled water and drying. However, this treatment stage leads to additional expenditures for the fabrication of displays, related to the need in special equipment and materials for this processing. Moreover, this treatment may lead to difficulties in removal polarizer from the sites of glued junctions.
Application of polarizers in displays bears certain peculiarities related to their small thickness and hydroscopicity, as well as to the contemporary techniques of display manufacturing (B. Bahadur, Editor, “Liquid Crystals applications and uses”, vol. 1, World Scientific, N.-Y., July (1990)). Thus, for example, in case of external positioning of polarizers, they have to be protected by some means to prevent their mechanical damage. Moreover, the area, covered by the protective layer, should be larger than the area of the polarizer in order to completely avoid any contact of the polarizer with the surroundings and prevent penetration of moisture. In case of their placement inside the cell, polarizer should not be around the perimeter of the cell at the areas of sealing since it will compromise the quality of the sealing, and will contact the surroundings. Therefore, polarizer should cover only the working area of the display and should not be at its periphery. Taking into account that several displays are formed on a single substrate, a necessity to form a pattern on its surface arises. This could be performed by localized application of polarizer onto the substrate, or by the localized removal of the polarizing layer applied previously on the entire area of the substrate, preserving it on the proper regions of the substrate.
Various methods of application of the herein films and machinery allowing its implementation are known (RU 21148884). Application of LC solution could be implemented using slot, rod or roller. However, the known apparatuses do not allow obtaining polarizers with reproducible characteristics because of the difficulties of forming a uniform 15–10 μm thickness wet layer film without lines and with uniform orientation of molecules over the entire working field of the substrate. Besides that, these apparatuses do not allow obtaining polarizers with polarizing layer applied on separate regions of the substrate.
There are known methods of forming a pattern of polarizing films based on lyotropic liquid crystal (LLC) compounds (RU 2110818). According to this prior art, the film is formed by a cylindrical engraved roller, in which the engraving is implemented as grooves on the surface of the roller within the boundaries of the pattern. The grooves get filled with LLC solution, which subsequently is transferred onto the surface of the substrate via rolling the roller over it. This method has the disadvantage that due to the high viscosity of the LLC, a roller with the diameter of no larger than 3 cm can be used to ensure quality of application. Therefore it is difficult to form patterns with linear dimensions along the direction of application larger than 10 cm. Besides that, the use of this method strongly depends on viscosity of LLC and the thickness of the forming film. In particular, the degree of orientation of molecules in thick films appears to be substantially worse than in thin ones. Therefore, in order to form a pattern on a polarizer, it is favorable to apply a layer of polarizer on the entire area of the substrate and later locally remove it from a part of the area, leaving the proper configuration of the polarizer.
Various methods of removing thin isotropic films from the surface of a substrate are known, either through mechanical removal on separate areas or using protective mask and etching (Physicochemical Methods for Processing Semiconductors (in Russian), B. D. Luft (ed.), Radio i Svyaz, Moscow, 1982, p. 107). However, all of them have a number of substantial disadvantages which limit their applicability for removal of polarizing layers. In particular, the mechanical method requires frequent replacement or cleaning of the removed material from the working element, and constant evacuation of the dust formed in the process of operation. The methods of local removal of polarizing layer via etching or rinsing with the use of protective mask are less productive and more expensive since they include several additional technological stages, related to formation of the protective mask. In addition, the application of the protective mask onto the polarizing layer and its subsequent removal invariably leads to worsening of the polarizer's structure.
U.S. Pat. No. 5,335,681 describes an apparatus for processing flat plate surfaces with technological fluids. This apparatus can be also used for partial removal of applied polarizing layer. A part of the polarizer film surface is treated with an appropriate solvent, and the dissolved material is removed by a vacuum pump. The solvent is supplied to the preset regions via injectors mounted above a moving plate. The main disadvantage of this technique is that the solvent is applied from injectors onto the open surface of a moving plate. This requires the plate velocity and the solvent supply rate to be controlled so as to confine the process within a preset region from which the coating has to be removed. This hinders precise treatment of small surface areas. To prevent spraying of the working fluid, the apparatus is provided with limiters determining boundaries of the treatment zone, which slide over the plate surface in the course of processing. However, these moving parts can produce damage of the plate surface and the layers formed prior to the polarizer application. This may negatively influence the functional properties of devices and, in particular, lead to damage of the conducting layers and decrease in the useful yield. In addition, use of the described apparatus reduces the production efficiency and increases expenditures in cases when the polarizing coating has to be removed in various directions, for example, in regions of complicated shape.